Apple targeted Samsung with a major lawsuit on April 18. The company claimed that Samsung's Galaxy-series of Android-based smartphones and tablets infringe on Apple's iOS-related software, hardware, and design patents, as well as iOS-related trademarks and trade dress. In addition to claiming Samsung copied the iPhone's physical design, Apple noted that the TouchWiz interface violated design patents and trademarks, and even copied the iPhone trade dress down to its box design.

"Rather than innovate and develop its own technology and a unique Samsung style for its smart phone products and computer tablets, Samsung chose to copy Apple's technology, user interface and innovative style in these infringing products," Apple wrote in its complaint.

Later that week, Apple COO Tim Cook explained that while Apple enjoys a good relationship with Samsung as a component supplier, its mobile communication division had "crossed the line" with the Galaxy S, Galaxy Tab, and its TouchWiz Android mod. "After trying for some time to work on the issue, we decided we needed to rely on the courts," Cook told analysts during the company's most recent quarterly earnings call.

Days later, Samsung filed three separate patent infringement lawsuits in South Korea, Japan, and Germany. Those lawsuits allege that Apple's iPhone uses Samsung intellectual property to connect to and improve communications with cell towers. Samsung implied that Apple was trying to bully a successful competitor, with company chairman Lee Kun-hee telling the press that "[w]hen a nail sticks out, [people] try to pound it down."

Samsung's US lawsuit targets the iPhone, which allegedly violates 10 Samsung patents that "relate to fundamental innovations that increase mobile device reliability, efficiency, and quality, and improve user interface in mobile handsets and other products." Though Apple has an extensive patent portfolio of its own, Bloomberg News noted that Samsung was awarded the second largest number of US patents in 2010 (IBM was at the top of the list).

Apple is no stranger to smartphone-related patent fights; the company is currently involved in lawsuits with HTC, Nokia, and Motorola, following through on its January 2010 warning to handset makers that it was prepared to file lawsuits over iPhone-related IP.

UPDATE: Former IP attorney Nilay Patel got his hands on Samsung's complaint and looked at the patents it is asserting against Apple. Seven are UMTS/W-CMDA "3G" related, while three are UI-related. Patel's analysis suggests that the seven 3G patents could be trumped by FRAND requirements if "essential" to 3G technology, or otherwise difficult to prove that the iPhone infringes. The UI-related patents seem fairly weak and "anti-climatic" compared to Apple's lawsuit, Patel wrote.